Rotating electric machine

ABSTRACT

In a rotating electric machine, a stator includes a stator core having slots formed therein and a stator coil comprised of phase windings each of which includes in-slot portions and turn portions. The turn portions of the phase windings together constitute a coil end part of the stator coil. Further, a cooling mechanism is provided to drop liquid coolant onto the coil end part. Moreover, the turn portions of the phase windings include long-pitch turn portions and short-pitch turn portions. In the coil end part, there are axially-overlapping pairs of the long-pitch and short-pitch turn portions over an entire circumferential range of the stator coil. For each axially-overlapping pair of the long-pitch and short-pitch turn portions, the short-pitch turn portion is located axially inside the long-pitch turn portion and faces the long-pitch turn portion through a void space formed therebetween over entire lengths of the long-pitch and short-pitch turn portions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese Patent Application No. 2015-30649 filed on Feb. 19, 2015, the content of which is hereby incorporated by reference in its entirety into this application.

BACKGROUND

1. Technical Field

The present invention relates to rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators.

2. Description of Related Art

There are known rotating electric machines that are used in motor vehicles as electric motors and electric generators. These rotating electric machines generally include a rotor and a stator. The stator includes an annular stator core and a stator coil. The stator core is disposed in radial opposition to the rotor and has a plurality of slots arranged in a circumferential direction thereof. The stator coil is comprised of a plurality of phase windings that an mounted on the stator core so as to be received in the slots of the stator core and be different in electrical phase from each other.

Japanese Patent Application Publication No. JP2011109894A (to be referred to as Patent Document 1 hereinafter) discloses a rotating electric machine which includes a three-phase stator coil 140 as shown in FIG. 16. The stator coil 140 is comprised of a plurality of phase windings mounted on a stator core 130. Each of the phase windings is formed of a plurality of substantially wave-shaped electric wires; each of the electric wires is configured with an electric conductor having a substantially rectangular cross-sectional shape and an insulating coat that covers the outer surface of the electric conductor. Moreover, each of the phase windings includes a plurality of in-slot portions 151C and a plurality of turn portions 152. Each of the in-slot portions 151C is received in one of slots 131 formed in the stator core 130. Each of the turn portions 152 is located outside the slots 131 of the stator core 130 to connect one pair of the in-slot portions 151C respectively received in two different ones of the slots 131. Moreover, each of the turn portions 152 includes an apex part 153 that is positioned at the center of the turn portion 152 in the extending direction of the turn portion 152 and extends in the circumferential direction of the stator core 130. Further, at the center of the apex part 153, there is formed a crank-shaped part 154 that is bent to radially offset the turn portion 152. Moreover, those turn portions 152 of the phase windings of the stator coil 140 which are located on a first axial side of the stator core 130 together constitute a first coil end part of the stator coil 140; those turn portions 152 of the phase windings of the stator coil 140 which are located on a second axial side of the stator core 130 together constitute a second coil end part of the stator coil 140.

More specifically, as shown in FIG. 16, the stator coil 140 is wave-wound on the stator core 130 so that each of the turn portions 152 connects a first in-slot portion 151C arranged at the Nth layer counting from the radially inside in a first slot 131 and a second in-slot portion 151C arranged at the (N−1)th layer counting from the radially inside in a second slot 131 that is away from the first slot 131 by six slot-pitches, where N is a natural number greater than or equal to 2.

However, in the rotating electric machine disclosed in Patent Document 1, the stator coil 140 generates heat upon being supplied with electric current, thereby lowering the efficiency of the rotating electric machine. Therefore, it is necessary to suitably cool the stator coil 140. To this end, liquid coolant may be supplied to drop onto the first and second coil end parts of the stator coil 140 which protrude respectively from opposite axial end faces of the stator core 130. In this case, if the liquid coolant dropped on the first and second coil end parts of the stator coil 140 could not effectively flow through the first and second coil end parts, it would be impossible to effectively cool the stator coil 140. Consequently, with an excessive increase in the temperature of the stator coil 140, the insulating coats of the electric wires forming the phase windings of the stator coil 140 might be fused, thus resulting in an insulation failure.

Japanese Patent Application Publication No. JPH11164506A (to be referred to as Patent Document 2 hereinafter) discloses a rotating electric machine which includes a three-phase stator coil 240 as shown in FIGS. 17-19. The stator coil 240 is comprised of a plurality of phase windings mounted on a stator core 130. Each of the phase windings is formed of a plurality of substantially U-shaped electric conductor segments; each of the electric conductor segments is configured with an electric conductor having a substantially rectangular cross-sectional shape and an insulating coat that covers the outer surface of the electric conductor. Moreover each of the phase windings includes a plurality of in-slot portions 151C and a plurality of turn portions 152. Each of the in-slot portions 151C is received in one of slots 131 formed in the stator core 130. Each of the turn portions 152 is located outside the slots 131 of the stator core 130 to connect one pair of the in-slot portions 151C respectively received in two different ones of the slots 131. Moreover each of the turn portions 152 includes an apex part 153 that is positioned at the center of the turn portion 152 in the extending direction of the turn portion 152 and extends in the circumferential direction of the stator core 130. Further, at the center of the apex part 153, there is formed a crank-shaped part 154 that is beat to radially offset the turn portion 152. Moreover, all the turn portions 152 of the phase windings of the stator coil 240 are located on the same axial side (i.e., the upper side in FIG. 17) of the stator core 130 and together constitute a coil end part of the stator coil 240.

More specifically, as shown in FIGS. 18-19, before being mounted to the stator core 130, each of the electric conductor segments is substantially U-shaped to have a pair of straight portions extending parallel to each other and a turn portion that connects ends of the straight portions on the same side. In forming the stator coil 240, the straight portions are axially inserted, from a first axial side (i.e., the upper side in FIG. 17) of the stator core 130, respectively into two slots 131 of the stator core 130 which are away from each other by six slot-pitches. Then, free end parts of the straight portions, which protrude outside the slots 131 on a second axial side (i.e., the lower side in FIG. 17) of the stator core 130, are twisted respectively toward opposite circumferential sides. Thereafter, each corresponding pair of distal ends of the twisted free end parts of the electric conductor segments are joined by, for example, welding. Consequently, in the resultant stator coil 240, those parts of the straight portions of the electric conductor segments which are received in the slots 131 of the stator core 130 respectively constitute the in-slot portions 151C of the phase windings of the stator coil 240; the turn portions of the electric conductor segments respectively constitute the turn portions 152 of the phase windings of the stator coil 240.

Moreover, according to Patent Document 2, the electric conductor segments forming the phase windings of the stator coil 240 are comprised of a plurality of large electric conductor segments 150A as shown in FIG. 18 and a plurality of small electric conductor segments 150B as shown in FIG. 19. The turn portions 152 of the large electric conductor segments 150A are larger than the turn portions 152 of the small electric conductor segments 150B. In each of the slots 131 of the stator core 130, there received four of the in-lot portions 151C of the electric conductor segments 150A and 150B in radial alignment with each other.

More specifically, as shown in FIG. 18, each of the large electric conductor segments 150A includes a first in-slot portion 151C arranged at the first layer (i.e., the innermost layer) in a first slot 131, a second in-slot portion 151C arranged at the fourth layer (i.e., the outermost layer) in a second slot 131 that is away from the first slot 131 by six slot-pitches, and one turn portion 152 that connects the first and second in-slot portions 151C. On the other hand, as shown in FIG. 19, each of the small electric conductor segments 150B includes a first in-slot portion 151C arranged at the second layer in a first slot 131, a second in-slot portion 151C arranged at the third layer in a second slot 131 that is away from the first slot 131 by six slot-pitches, and one turn portion 152 that connects the first and second in-slot portions 151C. Moreover, each joined-pair of the free and parts of the large and small electric conductor segments 150A and 150B respectively protrude from two slots 131 that are away from each other by six slot-pitches.

However, in the rotating electric machine disclosed in Patent Document 2, the stator coil 240 generates heat upon being supplied with electric current, thereby lowering the efficiency of the rotating electric machine. Therefore, it is necessary to suitably cool the stator coil 240. To this end, liquid coolant may be supplied to drop onto the coil end part of the stator coil 240 which protrudes from an axial end face of the stator core 130. In this case, if the liquid coolant dropped on the coil end part of the stator coil 240 could not effectively flow through the coil end part, it would be impossible to effectively cool the stator coil 240. Consequently, with an excessive increase in the temperature of the stator coil 240, the insulating coats of the electric conductor segments forming the phase windings of the stator coil 240 might be fused, thus resulting in an insulation failure.

SUMMARY

According to one exemplary embodiment, there is provided a rotating electric machine which includes a rotor, a stator and a cooling mechanism. The stator includes an annular stator core and a stator coil. The stator core is disposed in radial opposition to the rotor and has a plurality of slots arranged in a circumferential direction of the stator core. The stator coil is comprised of a plurality of phase windings mounted on the stator core. Each of the phase windings includes a plurality of in-slot portions and a plurality of turn portions. Each of the in-slot portions is received in one of the slots of the stator core. Each of the turn portions is located outside the slots of the stator core to connect one pair of the in-slot portions respectively received in two different ones of the slots. The turn portions together constitute a coil end part of the stator coil on at least one axial side of the stator core. The cooling mechanism is configured to drop liquid coolant onto the coil end part, thereby cooling the stator coil. The turn portions of the phase windings of the stator coil include, at least, a plurality of first-type turn portions and a plurality of second-type turn portions that have a smaller length than the first-type turn portions. In the coil end part of the stator coil, there are axially-overlapping pairs of the first-type and second-type turn portions over an entire circumferential range of the stator coil. For each axially-overlapping pair of the first-type and second-type turn portions, the second-type turn portion is located axially inside the first-type turn portion and faces the first-type turn portion through a void space formed therebetween over entire lengths of the first-type and second-type turn portions.

With the above configuration, the liquid coolant dropped on the coil and part will flow through the void space between each axially-overlapping pair of the first-type and second-type turn portions, thereby cooling the first-typo and second-type turn portions over the entire lengths thereof. Consequently, it is possible to effectively cool the stator coil.

In further implementations, each of the phase windings of the stator coil may have a substantially rectangular cross section and an insulating coat formed on its outer surface. In this case, it is preferable that for each axially-overlapping pair of the first-type and second-type turn portions, corresponding pairs of flat side surfaces of the first-type and second-type turn portions extend parallel to and face each other. Further, it is also preferable that each of the first-type and second-type turn portions is rounded at four corners of the rectangular cross section to have arc-shaped corners. Furthermore, it is also preferable that each of the first-type and second-type turn portions has four recesses each of which is formed at a central portion of one of four sides of the rectangular cross section so as to be recessed inward from other portions of the side.

Each of the first-type and second-type turn portions may have an apex part and a pair of oblique parts. The apex part is furthest in the turn portion from an axial end face of the stator core and extends in the circumferential direction of the stator core. The oblique parts are respectively formed on opposite sides of the apex part so as to extend obliquely with respect to the axial end face of the stator core at a predetermined oblique angle. In this case, it is preferable that the predetermined oblique angle is set to be the same for all the first-type and second-type turn portions.

In each of the slots of the stator core, there may be received at least four of the in-slot portions of the phase windings of the stator coil in radial alignment with each other. In this case, it is preferable that each of the turn portions of the phase windings of the stator coil connects the in-slot portion arranged at the Kth layer counting from the radially inside in one of the slots of the stator core and the in-slot portion arranged at the (K−1)th layer counting from the radially inside in another one of the slots, where K is an even number not less than 2.

It is also preferable that each of the first-type turn portions has a circumferential length of (M+1) slot-pitches while each of the second-type turn portions has a circumferential length of (M−1) slot-pitches, where M is a natural number not less than 2.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of one exemplary embodiment, which, however, should not be taken to limit the present invention to the specific embodiment but are for the purpose of explanation and understanding only.

In the accompanying drawings:

FIG. 1 is a partially cross-sectional view of a rotating electric machine according to the exemplary embodiment;

FIG. 2 is a perspective view of part of a stator of the rotating electric machine;

FIG. 3 is a partially cross-sectional view of part of the stator;

FIG. 4 is a perspective view of a pair of large and small electric conductor segments used for forming a stator coil of the stator;

FIG. 5 is a perspective view of part of the small electric conductor segment;

FIG. 6 is a cross-sectional view illustrating the configuration of the electric conductor segments used for forming the stator coil;

FIG. 7 is a circumferential development view illustrating the arrangement of the electric conductor segments in slots of a stator come of the stator;

FIG. 8 is a schematic circuit diagram of the stator coil;

FIG. 9 is a schematic view illustrating the arrangement of the pair of large and small electric conductor segments in the stator;

FIG. 10 is a cross-sectional view taken along the line X-X in FIG. 9;

FIG. 11 is a schematic view illustrating the flow of liquid coolant dropped on a first coil end part of the stator coil;

FIG. 12 is a schematic view illustrating the flow of the liquid coolant through turn portions of a U-phase winding of the stator coil;

FIG. 13 is a schematic view illustrating the flow of the liquid coolant through one axially-overlapping pair of the turn portions;

FIG. 14 is a schematic view illustrating the flow of liquid coolant through one pair of turn portions according to a comparative example;

FIG. 15 is a cross-sectional view illustrating a modification of the configuration of the electric conductor segments used for forming the stator coil;

FIG. 16 is a perspective view of part of a first conventional stator;

FIG. 17 is a perspective view of part of a second conventional stator;

FIG. 18 is a perspective view of large electric conductor segments used for forming a stator coil of the second conventional stator; and

FIG. 19 is a perspective view of small electric conductor segments used for forming the stator coil of the second conventional stator.

DESCRIPTION OF EMBODIMENT

FIG. 1 shows the overall configuration of a rotating electric machine 1 according to an exemplary embodiment.

The rotating electric machine 1 is designed to be used in a motor vehicle, such as a passenger car or truck, as an electric motor.

As shown in FIG. 1, the rotating electric machine 1 includes a housing 10, a rotor 14 and a stator 20. The housing 10 is comprised of a pair of cup-shaped housing pieces 10 a and 10 b which are jointed together at the open ends thereof. The housing 10 has a pair of bearings 11 and 12 mounted therein, via which a rotating shaft 13 is rotatably supported by the housing 10. The rotor 14 is received in the housing 10 and fixed on the rotating shaft 13. The stator 20 is fixed in the housing 10 so as to surround the radially outer periphery of the rotor 14.

Moreover, the rotating electric machine 1 further includes a coolant supplier for supplying liquid coolant to a three-phase stator coil 40 of the stator 20. The coolant supplier includes a pair of nozzles 15 and 16 for dropping the liquid coolant onto the stator coil 40. Specifically, the nozzle 15 is mounted to the housing piece 10 b so as to penetrate an axial end wall (i.e., a right end wall in FIG. 1) of the housing piece 10 b. The nozzle 15 has a discharge outlet 15 a formed at its distal end. The discharge outlet 15 a is located vertically above a first coil end part 45 of the stator coil 40, so as to discharge the liquid coolant to a central uppermost portion of the first coil end part 45. Similarly, the nozzle 16 is mounted to the housing piece 10 a so as to penetrate an axial end wall (i.e., a left and wall in FIG. 1) of the housing piece 10 a. The nozzle 16 has a discharge outlet 16 a formed at its distal end. The discharge outlet 16 a is located vertically above a second coil end part 46 of the stator coil 40, so as to discharge the liquid coolant to a central uppermost portion of the second coil end part 46.

Furthermore, in the present embodiment, the rotating electric machine 1 also includes a coolant collector a pump and a cooler, none of which are shown in the figures. The coolant collector collects the liquid coolant discharged out of the discharge outlets 15 a and 16 a of the nozzles 15 and 16 of the coolant supplier. The pump is provided to deliver the liquid coolant to the coolant supplier. The cooler is provided to cool the liquid coolant which has been heated when passing through the stator coil 40 and collected by the coolant collector. The coolant supplier, the coolant collector, the pump and the cooler together form a liquid coolant circulation circuit for circuiting the liquid coolant. In other words, the coolant supplier, the coolant collector, the pump and the cooler together constitute a cooling mechanism for cooling the stator coil 40.

In addition, in the present embodiment, ATF (Automotive Transmission Fluid) is used as the liquid coolant. However, it should be appreciated that other conventional liquid coolants, such as cooling oil, may also be used instead of ATF.

The rotor 14 includes a plurality of permanent magnets that form a plurality of magnetic poles on the radially outer periphery of the rotor 14 facing the radially inner periphery of the stator 20. The polarities of the magnetic poles alternate between north and south in the circumferential direction of the rotor 14. The number of the magnetic poles can be suitably set according to the design specification of the rotating electric machine 1. In the present embodiment, the number of the magnetic poles is set to be equal to, for example, eight (i.e., four north poles and four south poles).

Referring now to FIGS. 2 and 3, the stator 20 includes an annular (or hollow cylindrical) stator core 30, which is disposed radially outside the rotor 14 so as to surround the rotor 14, and the three-phase stator coil 40 mounted on the stator core 30. In addition, the stator 20 may further have insulating paper interposed between the stator core 30 and the stator coil 40.

In the present embodiment, the stator core 30 is formed by laminating a plurality of annular magnetic steel sheets in the axial direction of the stator core 30 and fixing them together by, for example, staking. In addition, between each adjacent pair of the magnetic steel sheets, there is interposed an insulating film. It should be appreciated that other conventional metal sheets may also be used instead of the magnetic steel sheets.

Moreover, as shown in FIGS. 2 and 3, the stator core 30 includes an annular back core 33, a plurality of stator teeth 34 and a plurality of slots 31. The stator teeth 34 each extend radially inward from the back core 33 and are circumferentially spaced at a predetermined pitch. Each of the slots 31 is formed between one circumferentially-adjacent pair of the stator teeth 34. Accordingly, the slots 31 are circumferentially arranged at the same predetermined pitch as the stator teeth 34. Moreover, each of the slots 31 extends in the axial direction of the stator core 30 so as to axially penetrate the stator core 30 and opens on the radially inner surface of the stator core 30. In addition, for each of the slots 31, the depth direction of the slot 31 coincides with a radial direction of the stator core 30.

In the present embodiment, there are provided two slots 31 per magnetic pole of the rotor 14 that has the eight magnetic poles and per phase of the three-phase stator coil 40. In other words, the slot multiplier number is set to 2. Accordingly, the total number of the slots 31 provided in the stator core 30 is equal to 48 (i.e., 2×8×3). In addition, as shown in FIG. 2, the forty-eight slots 31 are comprised of pairs of U-phase slots U1 and U2, V-phase slots V1 and V2 and W-phase slots W1 and W2 which are sequentially and repeatedly arranged in the circumferential direction of the stator core 30.

The stator coil 40 is comprised of a U-phase winding 41U, a V-phase winding 41V and a W-phase winding 41W (see FIG. 8), which are mounted on the stator core 30 so as to be received in the slots 31 of the stator corn 30 and be different in electrical phase from each other.

Each of the phase windings of the stator coil 40 includes a plurality of in-slot portions 51C and a plurality of turn portions 52A and 52B. Each of the in-slot portions 51C is received in one of the slots 31 of the stator core 30. Each of the turn portions 52A and 52B is located outside the slots 31 of the stator core 30 to connect one pair of the in-slot portions 51C respectively received in two different ones of the slots 31.

In the present embodiment, the stator coil 40 is formed by: (1) inserting a plurality of substantially U-shaped electric conductor segments 50 into the slots 31 of the stator core 30 from a first axial side of the stator core 30; (2) twisting free end parts of each of the electric conductor segments 50, which protrude outside the slots 31 of the stator core 30 on a second axial side of the stator core 30, respectively toward opposite circumferential sides; and (3) joining each corresponding pair of distal ends of the twisted free end parts of the electric conductor segments 50 by, for example, welding. Consequently, all the electric conductor segments 50 are electrically connected in a predetermined pattern, forming the stator coil 40.

Furthermore, in the present embodiment, as shown in FIG. 4, the electric conductor segments 50 forming the stator coil 40 are comprised of a plurality of large electric conductor segments 50A and a plurality of small electric conductor segments 50B that have a smaller size than the large electric conductor segments 50A. The large and small electric conductor segments 50A and 50B are formed by press-shaping an electric conductor wire, which has a substantially rectangular cross section, into the substantially U-shape using shaping dies. It should be noted that the shaping dies used for forming the large electric conductor segments 50A are different from those used for forming the small electric conductor segments 50B.

Each of the large electric conductor segments 50A has a pair of straight portions 51A extending parallel to each other and a turn portion 52A that connects ends of the straight portions 51A on the same side. On the other hand, each of the small electric conductor segments 50B has a pair of straight portions 51B extending parallel to each other and a turn portion 52B that connects ends of the straight portions 51B on the same side. The turn portions 52B of the small electric conductor segments 50B have a smaller length than the turn portions 52A of the large electric conductor segments 50A.

More specifically, in the present embodiment, the turn portions 52A of the large electric conductor segments 50A are formed to have a circumferential length of seven slot-pitches. On the other hand, the turn portions 52B of the small electric conductor segments 50B are formed to have a circumferential length of five slot-pitches. Accordingly, the turn portions 52A of the large electric conductor segments 50A may be referred to as long-pitch turn portions 52A; the turn portions 52B of the small electric conductor segments 50B may be referred to as short-pitch turn portions 52B.

Moreover, each of the turn portions 52A of the large electric conductor segments 50A includes an apex part 53A that is positioned at the center of the turn portion 52A in the extending direction of the turn portion 52A (or in the circumferential direction of the stator core 30) and furthest in the turn portion 52A from a first axial end face 30 a of the stator core 30; the first axial end face 30 a is on the first axial side of the stator care 30. The apex part 53A extends in the circumferential direction of the stator core 30 and parallel to the first axial end face 30 a of the stator core 30. Further, at the center of the apex part 53A, there is formed, by press-shaping, a crank-shaped part 54A that is bent to radially offset the turn portion 52A. The amount of radial offset made by the crank-shaped part 54A is set to be substantially equal to the radial thickness of the large and small electric conductor segments 50A and 50B. Similarly, each of the turn portions 52B of the small electric conductor segments 50B includes an apex part 53B that is positioned at the center of the turn portion 52B in the extending direction of the turn portion 52B (or in the circumferential direction of the stator core 30) and furthest in the turn portion 52B from the first axial end face 30 a of the stator core 30. The apex part 53B extends in the circumferential direction of the stator core 30 and parallel to the first axial end face 30 a of the stator core 30. Further, at the center of the apex part 53B, there is formed, by press-shaping, a crank-shaped part 54B that is bent to radially offset the turn portion 52B. The amount of radial offset made by the crank-shaped part 54B is also set to be substantially equal to the radial thickness of the large and small electric conductor segments 50A and 50B.

Furthermore each of the turn portions 52A of the large electric conductor segments 50A also includes a pair of oblique parts 55A that are respectively formed on opposite sides of the apex part 53A so as to extend obliquely with respect to the first axial end face 30 a of the stator core 30 at a first predetermined oblique angle θ1 (see FIG. 9). Each of the turn portions 52A of the large electric conductor segments 50A further includes a pair of bent parts 56A. Each of the bent parts 56A is formed, by press-shaping using shaping dies, substantially into the shape of a “<” character between one of the oblique parts 55A and one of the straight portions 51A connected by the turn portion 52A. The bent parts 56A protrude from the first axial end face 30 a of the stator core 30. Similarly, each of the turn portions 52B of the small electric conductor segments 50B also includes a pair of oblique parts 55B that are respectively formed on opposite sides of the apex part 53B so as to extend obliquely with respect to the first axial and face 30 a of the stator core 30 at a second predetermined oblique angle θ2 (see FIG. 9). Each of the turn portions 52B of the small electric conductor segments 50B further includes a pair of bent parts 56B. Each of the beat parts 56B is formed, by press-shaping using shaping dies, substantially into the shape of the “<” character between one of the oblique parts 55B and one of the straight portions 51B connected by the turn portion 52B. The bent parts 56B protrude from the first axial end face 30 a of the stator core 30 (see FIG. 5). In addition, in the present embodiment, the first predetermined oblique angle θ1 and the second predetermined oblique angle θ2 are set to be equal to each other (see FIG. 9).

In the present embodiment, as shown in FIG. 6, each of the large and small electric conductor segments 50A and 50B is configured with an electric conductor 58 and an insulating coat 59 that covers the outer surface of the electric conductor 58. The electric conductor 58 has a substantially rectangular cross section. The insulating coat 59 is two-layer structured to include an inner layer 59 a and an outer layer 59 b. In addition, at least the turn portions 52A and 52B of the large and small electric conductor segments 50A and 50B are rounded at the four corners of the rectangular cross section to have arc-shaped corners 50 c.

Next, the arrangement of the large and small electric conductor segments 50A and 50B in the slots 31 of the stator core 30 will be described with reference to FIG. 7.

In addition, for the sake of simplicity, in FIG. 7, there are shown only two pairs of U-phase slots U1 and U2 in which the U-phase winding 41U of the stator coil 40 is received. In the present embodiment, since the slot multiplier number is set to 2, the U-phase slots U1 are circumferentially spaced at six slot-pitches and the U-phase slots U2 are also circumferentially spaced at six slot-pitches.

For one of the large electric conductor segments 50A, one of the two straight portions 51A of the large electric conductor segment 50A is arranged at the first layer counting from the radially inside in one of the U-phase slots U1; the other straight portion 51A is arranged at the second layer counting from the radially inside in that one of the U-phase slots U2 which is away from the one of the U-phase slots U1 by seven slot-pitches in the clockwise direction (i.e., the X direction in FIG. 7). On the other hand, for one of the small electric conductor segments 50B, one of the two straight portions 51B of the small electric conductor segment 50B is arranged at the first layer counting from the radially inside in one of the U-phase slots U2; the other straight portion 51B is arranged at the second layer counting from the radially inside in that one of the U-phase slots U1 which is away from the one of the U-phase slots U2 by five slot-pitches in the clockwise direction.

Consequently, the long-pitch turn portion 52A of the large electric conductor segment 50A and the short-pitch turn portion 52B of the small electric conductor segment 50B are arranged to overlap each other in the axial direction of the stator core 30, with a predetermined void space S formed therebetween (see FIG. 9). Moreover, the short-pitch turn portion 52B of the small electric conductor segment 50B is located axially inside the long-pitch turn portion 52A of the large electric conductor segment 50A and faces the long-pitch turn portion 52A through the void space S formed therebetween over the entire lengths of the long-pitch and short-pitch turn portions 52A and 52B.

The above arrangement of the large and small electric conductor segments 50A and 50B is repeated at the first and second layers in all the pairs of U-phase slots U1 and U2. Moreover, though not shown in the figures, the large and small electric conductor segments 50A and 50B are also arranged at the first and second layers in the pain of V-phase slots V1 and V2 and at the first and second layers in the pairs of W-phase slots W1 and W2 in the same manner as at the first and second layers in the pairs of U-phase slots U1 and U2.

Further, for one of the large electric conductor segments 50A, one of the two straight portions 51A of the large electric conductor segment 50A is arranged at the third layer counting from the radially inside in one of the U-phase slots U1; the other straight portion 51A is arranged at the fourth layer counting from the radially inside in that one of the U-phase slots U2 which is away from the one of the U-phase slots U1 by seven slot-pitches in the clockwise direction (i.e., the X direction in FIG. 7). On the other hand, for one of the small electric conductor segments 50B, one of the two straight portions 51B of the small electric conductor segment 50B is arranged at the third layer counting from the radially inside in one of the U-phase slots U2; the other straight portion 51B is arranged at the fourth layer counting from the radially inside in that one of the U-phase slots U1 which is away from the one of the U-phase slots U2 by five slot-pitches in the clockwise direction.

The above arrangement of the large and small electric conductor segments 50A and 50B is repeated at the third and fourth layers in all the pairs of U-phase slots U1 and U2. Moreover, though not shown in the figures, the large and small electric conductor segments 50A and 50B are also arranged at the third and fourth layers in the pairs of V-phase slots V1 and V2 and at the third and fourth layers in the pairs of W-phase slots W1 and W2 in the same manner as at the third and fourth layers in the pairs of U-phase slots U1 and U2.

Furthermore, for one of the large electric conductor segments 50A, one of the two straight portions 51A of the large electric conductor segment 50A is arranged at the fifth layer counting from the radially inside in one of the U-phase slots U1; the other straight portion 51A is arranged at the sixth layer counting from the radially inside in that one of the U-phase slots U2 which is away from the one of the U-phase slots U1 by seven slot-pitches in the clockwise direction (i.e., the X direction in FIG. 7). On the other hand, for one of the small electric conductor segments 50B, one of the two straight portions 51B of the small electric conductor segment 50B is arranged at the fifth layer counting from the radially inside in one of the U-phase slots U2; the other straight portion 51B is arranged at the sixth layer counting from the radially inside in that one of the U-phase slots U1 which is away from the one of the U-phase slots U2 by five slot-pitches in the clockwise direction.

The above arrangement of the large and small electric conductor segments 50A and 50B is repeated at the fifth and sixth layers in all the pairs of U-phase slots U1 and U2. Moreover, though not shown in the figures, the large and small electric conductor segments 50A and 50B are also arranged at the fifth and sixth layers in the pairs of V-phase slots V1 and V2 and at the fifth and sixth layers in the pairs of W-phase slots W1 and W2 in the same manner as at the fifth and sixth layers in the pairs of U-phase slots U1 and U2.

Consequently, in each of the U-phase slots U1 and U2, V-phase slots V1 and V2 and W-phase slots W1 and W2, the are arranged a total of six straight portions 51A and 51B of the large and small electric conductor segments 50A and 50B in radial alignment with each other. More particularly, in the present embodiment, in each of the U-phase slots U1 and U2, V-phase slots V1 and V2 and W-phase slots W1 and W2, three straight portions 51A of the large electric conductor segments 50A are arranged alternately with three straight portions 51B of the small electric conductor segments 50B in the radial direction of the stator core 30.

Moreover, for each of the large and small electric conductor segments 50A and 50B, free end parts of the straight portions of the electric conductor segment, which protrude outside the slots 31 of the stator core 30 on the second axial side (i.e., the lower side in FIG. 2) of the stator core 30, are twisted respectively toward opposite circumferential sides so as to extend obliquely at a predetermined angle with respect to a second axial end face 30 a of the stator core 30; the second axial end face 30 a is on the second axial side of the stator core 30. Consequently, the free end parts of the straight portions are respectively transformed into a pair of oblique portions (not shown) of the electric wire segment; the oblique portions have a circumferential length corresponding to substantially half a magnetic pole pitch. Thereafter, on the second axial side of the stator care 30, each corresponding pair of distal ends of the oblique portions of all the large and small electric conductor segments 50A and 50B are joined by, for example, welding. Consequently, all the large and small electric conductor segments 50A and 50B are electrically connected in the predetermined pattern, forming the stator coil 40.

Specifically, those parts of the straight portions 51A and 51B of the large and small electric conductor segments 50A and 50B which are received in the slots 31 of the stator core 30 respectively constitute the in-slot portions 51C of the phase windings 41U, 41V and 41W of the stator coil 40; the turn portions 52A and 52B of the large and small electric conductor segments 50A and 50B respectively constitute the turn portions 52A and 52B of the phase windings 41U, 41V and 41W of the stator coil 40. Moreover, each of the phase windings 41U, 41V and 41W of the stator coil 40 is formed of a predetermined number of the large and small electric conductor segments 50A and 50B that are electrically connected with one another. More specifically, each of the phase windings 41U, 41V and 41W of the stator coil 40 is wave-wound on the stator core 30 so that the in-slot portion 51C of the phase winding which is arranged at the Nth layer counting from the radially inside in each of the slots 31 is electrically connected to the in-slot portion 51C of the phase winding which is arranged at the (N+1)th layer counting from the radially inside in another one of the slots 31, where N is a natural number not less than 1.

Moreover in the present embodiment, each of the turn portions 52A and 52B that constitute the first coil end part 45 of the stator coil 40 connects the in-slot portion 51C arranged at the Kth layer counting from the radially inside in one of the slots 31 and the in-slot portion 51C arranged at the (K−1)th layer counting from the radially inside in another one of the slots 31, where K is an even number not less than 2.

In addition, in the present embodiment, each of the phase windings 41U, 41V and 41W of the stator coil 40 extends along the circumferential direction of the stator core 30 by six turns. Therefore, each of the phase windings 41U, 41V and 41W also includes electric conductor segments (not shown) that are shaped differently from the above-described large and small electric conductor segments 50A and 50B. These differently-shaped electric conductor segments include, for example, electric conductor segments for forming output and neutral terminals of the phase winding and electric conductor segments for connecting different turns of the phase winding.

As shown in FIG. 8, in the present embodiment, the phase windings 41U, 41V and 41W of the stator coil 40 are star-connected to each other. Moreover, the U-phase winding 41U is comprised of four U-phase sub-windings U1, U2, U3 and U4 that am connected parallel to each other. The V-phase winding 41V is comprised of four V-phase sub-windings V1, V2, V3 and V4 that are connected parallel to each other. The W-phase winding 41W is comprised of four W-phase sub-windings W1, W2, W3 and W4 that are connected parallel to each other.

Moreover, as shown in FIG. 1, the stator coil 40 has the first coil end part 45 on the first axial side of the stator core 30 and the second coil end part 46 on the second axial side of the stator core 30; both the first and second coil end parts 45 and 46 are annular in overall shape. The first coil end part 45 is constituted of the turn portions 52A and 52B of the large and small electric conductor segments 50A and 50B which protrude from the first axial end face 30 a of the stator core 30. The second coil end part 46 is constituted of the oblique portions (or twisted free end parts) of the large and small electric conductor segments 50A and 50B which protrude from the second axial end face 30 a of the stator core 30.

In the present embodiment, as shown in FIG. 2, in the first coil end part 45 of the stator coil 40, there are circumferentially-adjacent pairs of the long-pitch and short-pitch turn portions 52A and 52B over the entire circumferential range of the stator coil 40. For each of the circumferentially-adjacent pairs of the long-pitch and short-pitch turn portions 52A and 52B, the apex parts 53A and 53B of the circumferentially-adjacent pair of the long-pitch and short-pitch turn portions 52A and 52B overlap each other in the axial direction of the stator core 30. Further, as shown in FIGS. 9-10, for each of the circumferentially-adjacent pairs of the long-pitch and short-pitch turn portions 52A and 52B, the short-pitch turn portion 52B is entirely located axial inside the long-pitch turn portion 52A; an axially-outer side surface 57B of the apex part 53B of the short-pitch turn portion 52B is covered by an axially-inner side surface 57A of the apex part 53A of the long-pitch turn portion 52A.

Moreover, in the first coil end part 45 of the stator coil 40, there are axially-overlapping pairs of the long-pitch and short-pitch turn portions 52A and 52B over the entire circumferential range of the stator coil 40. For each of the axially-overlapping pairs, the long-pitch and short-pitch turn portions 52A and 52B of the pair are arranged to overlap each other in the axial direction of the stator core 30, with the predetermined void space S formed therebetween (see FIG. 9). More specifically, the short-pitch turn portion 52B is located axially inside the long-pitch turn portion 52A and faces the long-pitch turn portion 52A through the void space S formed therebetween over the entire lengths of the long-pitch and short-pitch turn portions 52A and 52B. In addition, in the present embodiment, corresponding pairs of flat side surfaces of the long-pitch and short-pitch turn portions 52A and 52B extend parallel to and face each other.

Furthermore, each axially-overlapping pair of the apex parts 53A and 53B of the long-pitch and short-pitch turn portions 52A and 52B are of the same phase, in other words, are included in the same one of the U-phase, V-phase and W-phase windings 41U, 41V and 41W of the stator coil 40. More specifically, as shown in FIG. 2, each of the apex parts 53A (U) of the long-pitch turn portions 52A (U) of the U-phase winding 41U axially overlaps one of the apex parts 53B (U) of the short-pitch turn portions 52B (U) of the U-phase winding 41U. Each of the apex parts 53A (V) of the long-pitch turn portions 52A (V) of the V-phase winding 41V axially overlaps one of the apex parts 53B (V) of the short-pitch turn portions 52B (V) of the V-phase winding 41V. Each of the apex parts 53A (W) of the long-pitch turn portions 52A (W) of the W-phase winding 41W axially overlaps one of the apex parts 53B (W) of the short-pitch turn portions 52B (W) of the W-phase winding 41W.

Furthermore, as shown in FIGS. 9-10 and the region A of FIG. 2, for each axially-overlapping pair of the apex parts 53A and 53B, the axially-inner side surface 57A of the apex part 53A and the axially-outer side surface 57B of the apex part 53B are arranged parallel to and axially facing each other.

Moreover, as shown in FIG. 2, each circumferentially-adjacent pair of the apex parts 53A and 53B of the long-pitch and short-pitch tam portions 52A and 52B of all the phase windings 41U, 41V and 41W are circumferentially offset from each other by a distance greater than the predetermined pitch at which the slots 31 of the stator core 30 are arranged (i.e., greater than one slot-pitch). More specifically, in the present embodiment, each of the crank-shaped parts 54A formed in the apex parts 53A of the long-pitch turn portions 52A is circumferentially adjacent to and offset by two slot-pitches from another one of the crank-shaped parts 54A; each of the crank-shaped parts 54B formed in the apex parts 53B of the short-pitch turn portions 52B is circumferentially adjacent to and offset by two slot-pitches from another one of the crank-shaped parts 54B. Further, as shown in the region B of FIG. 2, each of the apex parts 53B of the short-pitch turn portions 52B is arranged to circumferentially neighbor on one of the straight-extending oblique parts 55A of the long-pitch turn portions 52A.

In addition, the circumferential length of the long-pitch turn portions 52A is set to (M+1) slot-pitches while the circumferential length of the short-pitch turn portions 52B is set to (M−1) slot-pitches, where M is a natural number greater than or equal to 2. More particularly, in the present embodiment, with M=6, the circumferential length of the long-pitch turn portions 52A is set to seven slot-pitches and the circumferential length of the short-pitch turn portions 52B is set to five slot-pitches.

Next, operation of the rotating electric machine 1 according to the present embodiment will be described.

In normal use, the rotating electric machine 1 is mounted at a predetermined position in the vehicle so that, the axial direction of the rotating shaft 13 coincides with a horizontal direction; and the discharge outlets 15 a and 16 a of the nozzles 15 and 16 of the coolant supplier are respectively located vertically above the first and second coil end parts 45 and 46 of the stator coil 40.

Upon supply of electric current to the stator coil 40 of the stator 20, the rotor 14 rotates in a predetermined direction. Moreover, with the rotation of the rotor 14, the rotating shaft 13 also rotates in the predetermined direction, driving other devices or components mechanically connected to the rotating shaft 13.

At the same time, the cooling mechanism for cooling the stator coil 40 starts operation, delivering the liquid coolant to the nozzles 15 and 16. Then, the liquid coolant is discharged from the discharge outlets 15 a and 16 a of the nozzles 15 and 16 to the first and second coil end parts 45 and 46 of the stator coil 40.

Hereinafter, the cooling of the first coil end part 45 by the liquid coolant will be described in detail. As described previously, the first coil end part 45 is constituted of the turn portions 52A and 52B of the large and small electric conductor segments 50A and 50B.

The liquid coolant, which is discharged from the discharge outlet 15 a of the nozzle 15, drops onto the central uppermost portion of the first coil end part 45, branches to both circumferential sides of the central uppermost portion, and flows downward.

Specifically, as shown in FIG. 11, the liquid coolant enters the void space S between each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B in the first coil end part 45. Then, the liquid coolant flows through the void space S while cooling the long-pitch and short-pitch turn portions 52A and 52B; the void space S is formed over the entire lengths of the long-pitch and short-pitch turn portions 52A and 52B.

For example, as shown in FIG. 12, the liquid coolant dropped on the outermost layer (i.e., the sixth layer) of the U-phase winding 41U first flows through the void space S formed between the upper halves (i.e., the left halves in FIG. 12) of a first axially-overlapping pair of the long-pitch and short-pitch turn portions 52A(U) and 52B(U) of the U-phase winding 41; the upper halves are located on the outermost layer. Then, the liquid coolant flows through the void space S formed between the lower halves (i.e., the right halves in FIG. 12) of the first axially-overlapping pair of the long-pitch and short-pitch turn portions 52A(U) and 52B(U); the lower halves are located on the fifth layer. That is, a layer change from the outermost layer to the fifth layer is made at the apex parts 53A and 53B of the first axially-overlapping pair of the long-pitch and short-pitch turn portions 52A(U) and 52B(U). Thereafter, the liquid coolant moves to and flows through the void space S formed between the upper halves of a second axially-overlapping pair of the long-pitch and short-pitch turn portions 52A(U) and 52B(U) of the U-phase winding 41U; the upper halves are located on the fourth layer. Then, the liquid coolant flows through the void space S formed between the lower halves of the second axially-overlapping pair of the long-pitch and short-pitch turn portions 52A(U) and 52B(U); the lower halves are located on the third layer. That is, a layer change from the fourth layer to the third layer is made at the apex parts 53A and 53B of the second axially-overlapping pair of the long-pitch and short-pitch turn portions 52A(U) and 52B(U).

In the above manner, in the upper half of the first coil end part 45, the liquid coolant flows through the void spaces S between axially-overlapping pairs of the long-pitch and short-pitch turn portions 52A(U) and 52B(U) of the U-phase winding 41U, moving layer by layer from the outermost layer to the innermost layer (i.e., the first layer).

Moreover, in the lower half of the first coil end part 45, the liquid coolant flows through the void spaces S between axially-overlapping pairs of the long-pitch and short-pitch turn portions 52A(U) and 52B(U) of the U-phase winding 41U, moving layer by layer from the innermost layer to the outermost layer. Finally, the liquid coolant drops down from the first coil end part 45 to the bottom of the housing 10.

In addition, though not shown in the figures, the V-phase and W-phase windings 41V and 41W of the stator coil 40 are also cooled by the liquid coolant in the same manner as the U-phase winding 41U. The liquid coolant dropping down to the bottom of the housing 10 is then collected by the coolant collector, cooled by the cooler, and delivered by the pump again to the nozzles 15 and 16.

As shown in FIG. 13, in the present embodiment, the first coil end part 45 is constituted of the long-pitch turn portions 52A and the short-pitch turn portions 52B that have a smaller length than the long-pitch turn portions 52A. Consequently, the liquid coolant flows through the void space S between each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B; the void space S is formed over the entire lengths of the long-pitch and short-pitch turn portions 52A and 52B. As a result, it is possible to effectively cool the long-pitch and short-pitch turn portions 52A and 52B over a wide range.

In contrast, in a comparative example as shown in FIG. 14, all of turn portions 152, which together constitute a coil end part protruding from an axial end face of a stator core 130, have the same length. Therefore, the turn portions 152 cannot be arranged in axially-overlapping pairs. Consequently, for each adjacent pair of the turn portions 152, liquid coolant flows through only a void space formed between the upper halves of the pair of the turn portions 152, leaving the pair of the turn portions 152 from the apex parts 153 thereof. As a result, the lower halves of the pair of the turn portions 152 cannot be cooled by the liquid coolant. That is to say, it is impossible to effectively cool the pair of the turn portions 152 over a wide range.

The above-described rotating electric machine 1 according to the present embodiment has the following advantages.

In the present embodiment, the rotating electric machine 1 includes the rotor 14, the stator 20 and the cooling mechanism. The stator 20 includes the annular stator core 30 and the three-phase coil 40. The stator core 30 is disposed in radial opposition to the rotor 14 and has the slots 31 arranged in the circumferential direction of the stator core 30. The stator coil 40 is comprised of the U-phase, V-phase and W-phase windings 41U, 41V and 41W mounted on the stator core 30. Each of the phase windings 41U, 41V and 41W includes the in-slot portions 51C and the turn portions 52A and 52B. Each of the in-slot portions 51C is received in one of the slots 31 of the stator core 30. Each of the turn portions 52A and 52B is located outside the slots 31 of the stator core 30 to connect one pair of the in-slot portions 51C respectively received in two different ones of the slots 31. The turn portions 52A and 52B together constitute the first coil end part 45 of the stator coil 40 on the first axial side of the stator core 30. The cooling mechanism includes the nozzle 15 to drop the liquid coolant onto the first coil end part 45, thereby cooling the stator coil 40. Moreover, in the present embodiment, the turn portions of the phase windings 41U, 41V and 41W of the stator coil 40 include the long-pitch turn portions 52A and the short-pitch turn portions 52B that have a smaller length than the long-pitch turn portions 52A. In the first coil end part 45 of the stator coil 40, there are axially-overlapping pairs of the long-pitch and short-pitch turn portions 52A and 52B over the entire circumferential range of the stator coil 40. For each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B, the short-pitch turn portion 52B is located axially inside the long-pitch turn portion 52A and faces the long-pitch turn portion 52A through the void space S formed therebetween over the entire lengths of the long-pitch and short-pitch turn portions 52A and 52B.

With the above configuration, the liquid coolant dropped on the first coil end part 45 will flow through the void space S between each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B, thereby cooling the long-pitch and short-pitch turn portions 52A and 52B over the entire lengths thereof. Consequently, it is possible to effectively cool the stator coil 40.

Moreover, in the present embodiment, each of the phase windings 41U, 41V and 41W of the stator coil 40 (more specifically, each of the large and small electric conductor segments 50A and 50B forming the phase windings 41U, 41V and 41W) has a substantially rectangular cross section and the insulating coat 59 formed on its outer surface (see FIG. 6). For each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B, corresponding pairs of the flat side surfaces of the long-pitch and short-pitch turn portions 52A and 52B extend parallel to and face each other (see FIG. 9).

With the above configuration, it is possible to keep, by surface tension, the liquid coolant flowing on the flat side surfaces of the long-pitch and short-pitch turn portions 52A and 52B, thereby improving the cooling performance.

Further, in the present embodiment, each of the long-pitch and short-pitch turn portions 52A and 52B is rounded at the four corners of the rectangular cross section to have the arc-shaped corners 50 c (see FIG. 6).

With the above configuration, it is possible to increase the amount of the liquid coolant flowing through the void space S between each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B, thereby further improving the cooling performance.

Furthermore, in the present embodiment, each of the long-pitch turn portions 52A has the apex part 53A and the oblique parts 55A. The apex part 53A is farthest in the long-pitch turn portion 52A from the first axial end face 30 a of the stator core 30 and extends in the circumferential direction of the stator core 30. The oblique parts 55A are respectively formed on opposite sides of the apex part 53A so as to extend obliquely with respect to the first axial end face 30 a of the stator core 30 at the first predetermined oblique angle θ1. Similarly, each of the short-pitch turn portions 52B has the apex part 53B and the oblique parts 55B. The apex part 53B is furthest in the short-pitch turn portion 52B from the first axial end face 30 a of the stator core 30 and extends in the circumferential direction of the stator core 30. The oblique parts 55B are respectively formed on opposite sides of the apex part 53B so as to extend obliquely with respect to the first axial end face 30 a of the stator core 30 at the second predetermined oblique angle θ1. Further, in the present embodiment, the first predetermined oblique angle θ1 and the second predetermined oblique angle θ2 are set to be equal to each other (see FIG. 9).

With the above configuration, it is possible to keep the size (or the width) of the void space S between each facing-pair of the side surfaces of the oblique parts 55A and 55B of the long-pitch and short-pitch turn portions 52A and 52B constant, thereby keeping the surface tension of the liquid coolant on the side surfaces of the oblique parts 55A and 55B constant. Consequently, it is possible to more reliably keep the liquid coolant flowing on the side surfaces of the oblique parts 55A and 55B, thereby farther improving the cooling performance.

In the present embodiment, in each of the slots 31 of the stator core 30, there are received six in-slot portions 51C of the phase windings 41U, 41V and 41W of the stator coil 40 (or six straight portions 51A and 51B of the large and small electric conductor segments 50A and 50B) in radial alignment with each other. Each of the turn portions 52A and 52B of the phase windings 41U, 41V and 41W connects the in-slot portion 51C arranged at the Kth layer counting from the radially inside in one of the slots 31 of the stator core 30 and the in-slot portion 51C arranged at the (K−1)th layer counting from the radially inside in another one of the slots 31, where K is an even number not less than 2.

With the above configuration, it is possible to allow the liquid coolant dropped on the first coil end part 45 of the stator coil 40 to flow through the void space S between each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B, moving layer by layer from the outermost layer to the innermost layer. Consequently, t is possible to effectively cool the entire first coil end part 45 of the stator coil 40.

In the present embodiment, each of the long-pitch turn portions 52A has the circumferential length of seven slot-pitches (i.e., (M+1) slot-pitches with M being 6), while each of the short-pitch turn portions 52B has the circumferential length of five slot-pitches (i.e., (M−1) slot-pitches with M being 6). Moreover, each of the apex parts 53B of the small-pitch turn portions 52B is located axially inside and axially overlaps one of the apex parts 53A of the long-pitch turn portions 52A.

With the above configuration, it is possible to improve the cooling performance without changing other characteristics in comparison with a conventional stator coil in which all the turn portions have the same circumferential length of M slot-pitches.

While the above particular embodiment has been shown and described, it will be understood by those skilled in the art that various modifications, changes, and improvements may be made without departing from the spirit of the present invention.

For example, in the above-described embodiment, each of the phase windings 41U, 41V and 41W of the stator coil 40 is formed of the large and small electric conductor segments 50A and 50B that have the substantially rectangular cross section (see FIG. 6).

However, as shown in FIG. 15, at least the turn portions 52A and 52B of the large and small electric conductor segments 50A and 50B (or at least the turn portions 52A and 52B of the phase windings 41U, 41V and 41W) may have four recesses 50 d each of which is formed at a central portion of one of the four sides of the rectangular cross section so as to be recessed inward from the other portions of the side. More specifically, at least the turn portions 52A and 52B of the large and small electric conductor segments 50A and 50B may be configured with an electric conductor 58 having a substantially rectangular cross-sectional shape and an insulating coat 59 that covers the outer surface of the electric conductor 58 and has the for recesses 50 d formed in its outer surface. In addition, the insulating coat 59 may also be rounded to have the four arc-shaped corners 50 c. In this case, it is possible to further increase the amount of the liquid coolant flowing through the void space S between each axially-overlapping pair of the long-pitch and short-pitch turn portions 52A and 52B, thereby further improving the cooling performance.

In the above-described embodiment, two types of turn portions having different circumferential lengths (i.e., the long-pitch turn portions 52A and the short-pitch turn portions 52B) are employed in the stator coil 40. Moreover, the number of the apex parts of the turn portions overlapping each other in the axial direction of the stator core 30 is equal to 2.

However, it is also possible to employ three or more types of turn portions having different circumferential lengths in the stator coil 40. In this case, the number of the apex parts of the turn portions overlapping each other in the axial direction of the stator core 30 would be accordingly equal to 3 or more.

In the above-described embodiment, each of the phase windings 41U, 41V and 41W of the stator coil 40 is formed of the substantially U-shaped large and small electric conductor segments 50A and 50B. The first coil end part 45 of the stator coil 40 is constituted of the turn portions 52A and 52B of the large and small electric conductor segments 50A and 50B which protrude from the first axial and face 30 a of the stator core 30. The second coil end part 46 of the stator coil 40 is constituted of the oblique portions (or twisted free end parts) of the large and small electric conductor segments 50A and 50B which protrude from the second axial end face 30 a of the stator core 30.

However, each of the phase windings 41U, 41V and 41W of the stator coil 40 may be alternatively formed of a plurality of substantially wave-shaped electric wires; each of the electric wires includes a plurality of in-slot portions 51C and a plurality of turn portions 52A and 52B. In this case, the first coil end part 45 of the stator coil 40 would be constituted of those turn portions 52A and 52B of the electric wires which protrude from the first axial end face 30 a of the stator core 30; the second coil end part 46 of the stator coil 40 would be constituted of those turn portions 52A and 52B of the electric wires which protrude from the second axial end face 30 a of the stator care 30.

In the above-described embodiment, the present invention is directed to the stator 20 of the rotating electric machine 1 that is designed to be used in a motor vehicle as an electric motor. However, the present invention can also be applied to stators of other rotating electric machines, such as a stator of an electric generator or a stator of a motor-generator that can selectively function both as an electric motor and as an electric generator. 

What is claimed is:
 1. A rotating electric machine comprising: a rotor; a stator including an annular stator core and a stator coil, the stator core being disposed in radial opposition to the rotor and having a plurality of slots arranged in a circumferential direction of the stator core, the stator coil being comprised of a plurality of phase windings mounted on the stator core, each of the phase windings including a plurality of in-slot portions and a plurality of turn portions, each of the in-lot portions being received in one of the slots of the stator core, each of the turn portions being located outside the slots of the stator core to connect one pair of the in-slot portions respectively received in two different ones of the slots, the turn portions together constituting a coil end part of the stator coil on at least one axial side of the stator core; and a cooling mechanism configured to drop liquid coolant onto the coil end part, thereby cooling the stator coil, wherein the turn portions of the phase windings of the stator coil comprise, at least, a plurality of first-type turn portions and a plurality of second-type turn portions that have a smaller length than the first-type turn portions, in the coil and part of the stator coil, there are axially-overlapping pairs of the first-type and second-type turn portions over an entire circumferential range of the stator coil, for each axially-overlapping pair of the first-type and second-type turn portions, the second-type turn portion is located axially inside the first-type turn portion and faces the first-type turn portion through a void space formed therebetween over entire lengths of the first-type and second-type turn portions.
 2. The rotating electric machine as set forth in claim 1, wherein each of the phase windings of the stator coil has a substantially rectangular cross section and an insulating coat formed on its outer surface, and for each axially-overlapping pair of the first-type and second-type turn portions, corresponding pairs of flat side surfaces of the first-type and second-type turn portions extend parallel to and face each other.
 3. The rotating electric machine as set forth in claim 2, wherein each of the first-type and second-type turn portions is rounded at four corners of the rectangular cross section to have arc-shaped corners.
 4. The rotating electric machine as set forth in claim 2, wherein each of the first-type and second-type turn portions has four recesses each of which is formed at a central portion of one of four sides of the rectangular cross section so as to be recessed inward from other portions of the side.
 5. The rotating electric machine as set forth in claim 1, wherein each of the first-type and second-type turn portions has an apex part and a pair of oblique parts, the apex part being furthest in the turn portion from an axial end face of the stator core and extending in the circumferential direction of the stator core, the oblique parts being respectively formed on opposite sides of the apex part so as to extend obliquely with respect to the axial end face of the stator core at a predetermined oblique angle, and the predetermined oblique angle is set to be the same for all the first-type and second-type turn portions.
 6. The rotating electric machine as set forth in claim 1, wherein in each of the slots of the stator core, there are received at least four of the in-slot portions of the phase windings of the stator coil in radial alignment with each other, and each of the turn portions of the phase windings of the stator coil connects the in-slot portion arranged at the Kth layer counting from the radially inside in one of the slots of the stator core and the in-slot portion arranged at the (K−1)th layer counting from the radially inside in another one of the slots, where K is an even number not less than
 2. 7. The rotating electric machine as set forth in claim 1, wherein each of the first-type turn portions has a circumferential length of (M+1) slot-pitches while each of the second-type turn portions has a circumferential length of (M−1) slot-pitches, where M is a natural number not less than
 2. 